This application claims priority to Japanese Patent Application No. 10-294071 filed on Oct. 15, 1998 and Japanese Patent Application No. 11-78343, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to battery packs. More particularly, the present invention relates to battery packs having battery cells that are disposed within a case and are used as power sources for electric power tools.
2. Description of the Related Art
Generally, battery packs for electric power tools include exposed electric terminals for charging and discharging the enclosed battery cells. When a battery pack is attached to an electric power tool, electrical contact is established between the terminals of the battery pack and the terminals of the battery holder in the tool, thus supplying power to the tool. When the charge level of a battery pack becomes low, the pack is set in a battery charger to establish electrical contact between the charging and discharging terminals of the pack and the charging terminals of the battery charger, thus recharging the battery cells in the pack.
When charging the battery cells in a battery pack, the temperature of the battery cells rises due to buildup of heat in the battery cells themselves and heat conduction from the transformer of the charger. In certain types of cells and batteries, such as nickel metal hydride cells, this phenomenon is so severe that the service life of the cells will be shortened unless some preventative measures are taken. One structure for preventing heat buildup in a battery pack is disclosed in Japanese Laid-open Utility Model Publication No. 6-54209. This structure includes within a charger a fan for delivering air to the terminals and air passages running through the cells in the battery pack and connecting openings provided in the battery pack case. When the battery pack is set in the charger, the fan sends air through the cells along the passages in order to prevent heat buildup in the battery cells.
Although the foregoing structure can significantly lessen the deterioration of the battery cells by preventing heat buildup in the battery cells, it suffers from other drawbacks. For example, moisture and other foreign matter can easily enter the battery pack through the openings in the battery pack and may rust the battery cells, which may cause leakage of the electrolyte. Furthermore, conductive foreign matter may cause a short-circuit. In order to solve problems caused by entry of foreign matter, Japanese Utility Model Publication No. 5-37634 discloses an improved combination of a battery pack and a charger. The battery pack is provided with interlocked doors that open when the pack is set on the charger and close when the pack is removed from the charger so as to keep out foreign matter. One significant drawback of this structure is an increase in the manufacturing cost due to the sliding doors and guide bosses protruding from the charger for opening and closing the doors. Moreover, the existence of the guide bosses limits the types of battery packs that can be recharged on the charger, thus reducing its general versatility. The durability and reliability of the mechanism for operating the sliding doors is somewhat questionable because the relatively fragile guide bosses may break when the battery pack is set on the charger.
In view of the above-identified problems, an important object of the present invention is to provide a battery pack having a simple structure for preventing both internal heat buildup and entry of foreign matter.
Another object of the present invention is to provide a battery pack having a simple structure for improving the durability of the battery pack by lessening vibration and impact on the cells.
The above objects and other related objects are realized by the invention, which provides a battery pack comprising: a first case containing a plurality of battery cells; radiator means disposed in contact with the cells within the first case and having at least one surface for radiating heat conducted from the battery cells; a first air passage defined at least partially by said at least one surface of the radiator means and separated from the battery cells; and at least one air outlet formed in the first case and connected with the first air passage. This structure itself (i.e., not in cooperation with any other structure, such as a charger) easily prevents heat buildup in the battery cells in the battery pack and prevents entry of foreign matter into the inner case, thus prolonging the service life of the battery cells and preventing leakage of the electrolytic solution and short-circuiting due to rusting.
According to another aspect of the present invention, the battery cells are divided into a plurality of blocks and there is at least one second passage provided between the blocks, the at least one second air passage being in communication with the first air passage. The second air passage is provided between the cell blocks and cools the cells more evenly; thus more effectively preventing deterioration of the battery cells.
According to another aspect of the present invention, the radiator means includes a plurality of ribs, which are oriented generally parallel to the direction of airflow through at least in one of the first and second air passages. Due to the ribs extending in the direction of cooling, airflow is provided on certain surfaces of the first and/or second air passages and heat is more effectively radiated from the battery cells.
According to yet another aspect of the present invention, the battery pack further comprises a second case that is smaller than the first case, contains the battery cells and is disposed within the first case. Furthermore, the first air passage may be formed between the first and second cases and elastic material may be interposed between the first and second cases. The aforementioned double casing structure effectively lessens transmission of impact and vibration to the battery cells, thus enhancing the durability of the battery pack.
According to still another aspect of the present invention, the battery pack further comprises an air inlet provided in the first case and connected with the first air passage. The first air passage is defined by inner surfaces of the first case and continuous recesses provided on outer surfaces of the second case.
In accordance with another aspect of the present invention, each of the first and second cases has a generally box-like shape. Moreover, the first air passage starts at the inlet provided in an upper surface of the first case, proceeds along a first inner side surface of the first case, forks into two branches along two opposite second and third inner side surfaces of the first case connected to the first inner side surface, and terminates at first and second air outlets provided in a fourth inner side surface of the first case.
In another embodiment, the second case includes first to fourth outer side surfaces corresponding to the first to fourth inner side surfaces of the first case, respectively. The radiator means is a radiator plate having a generally U-shaped cross section that continuously surrounds the first, second, and third outer surfaces of the second case. Further, the ribs may be formed on outer surfaces of the radiator plate in the first air passage.
In another embodiment, the elastic material is disposed along upper and lower edges of the first case such that the first air passage is hermetically isolated from the cells.
In another aspect, the cells are divided into two blocks and the radiator means includes first and second radiator plates arranged in parallel, each radiator plate having a generally U-shaped cross section and surrounding one of the cell blocks. Moreover, the second air passage is defined between the radiator plates.
In another aspect, the ribs are provided on outer surfaces of the first and second radiator plates in the second air passage.
In another embodiment, the battery pack of the invention further comprises a third air outlet provided in the fourth inner side surface of the first case between the first and second outlets. In this embodiment, a first end of the second air passage may be connected to the first air passage and a second end thereof is connected to the third air outlet.
To carry out the invention in one preferred mode, the second air passage is hermetically isolated from the cell blocks.